So, one thing I was disappointed about when I got my iPhone was how quickly the battery ran down. I would charge it over night and then have to put it on the charger for a little while while I was at the office to make sure it had juice for my drive home.
I made one change that seems to at least double the life of the battery. Previously, my Exchange account would automatically push email to me and the iPhone would regularly fetch email from my Gmail account. I changed both of these settings to Manual so that the accounts are not checked until I go into the Mail app.
This may not work for your needs, but in my world it’s not absolutely critical that I know the moment an email comes in. I just need the ability to check it while I’m out. And changing this setting means that I only need to charge my iPhone overnight.